Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias, voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,100 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,100 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The heating elements within each HO2S heat the sensor. This allows the system to enter Closed Loop earlier and the control module to calculate air-to-fuel ratio quicker.

If the powertrain control module (PCM) detects an active HO2S 1 signal of a lower than calibrated minimum amplitude, DTC P2A00 will set.

The HO2S 1 has the following circuits:

• A HO2S 1 high signal circuit
• A HO2S 1 low signal circuit
• A HO2S 1 heater ignition voltage circuit
• A HO2S 1 heater low control circuit